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[3.8] bpo-39562: Prevent collision of future and compiler flags (GH-19230) (GH-19835)
The constant values of future flags in the __future__ module is updated in order to prevent collision with compiler flags. Previously PyCF_ALLOW_TOP_LEVEL_AWAIT was clashing with CO_FUTURE_DIVISION.. (cherry picked from commit 4454057) Co-authored-by: Batuhan Taşkaya <batuhanosmantaskaya@gmail.com>
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‎Doc/whatsnew/3.8.rst‎

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@@ -2234,3 +2234,8 @@ Notable changes in Python 3.8.2
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Fixed a regression with the ``ignore`` callback of :func:`shutil.copytree`.
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The argument types are now str and List[str] again.
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(Contributed by Manuel Barkhau and Giampaolo Rodola in :issue:`39390`.)
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The constant values of future flags in the :mod:`__future__` module
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are updated in order to prevent collision with compiler flags. Previously
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``PyCF_ALLOW_TOP_LEVEL_AWAIT`` was clashing with ``CO_FUTURE_DIVISION``.
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(Contributed by Batuhan Taskaya in :issue:`39562`)

‎Include/code.h‎

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@@ -88,19 +88,19 @@ typedef struct {
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#define CO_ITERABLE_COROUTINE 0x0100
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#define CO_ASYNC_GENERATOR 0x0200
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/* These are no longer used. */
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#if 0
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#define CO_GENERATOR_ALLOWED 0x1000
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#endif
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#define CO_FUTURE_DIVISION 0x2000
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#define CO_FUTURE_ABSOLUTE_IMPORT 0x4000 /* do absolute imports by default */
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#define CO_FUTURE_WITH_STATEMENT 0x8000
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#define CO_FUTURE_PRINT_FUNCTION 0x10000
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#define CO_FUTURE_UNICODE_LITERALS 0x20000
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#define CO_FUTURE_BARRY_AS_BDFL 0x40000
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#define CO_FUTURE_GENERATOR_STOP 0x80000
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#define CO_FUTURE_ANNOTATIONS 0x100000
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/* bpo-39562: These constant values are changed in Python 3.9
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to prevent collision with compiler flags. CO_FUTURE_ and PyCF_
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constants must be kept unique. PyCF_ constants can use bits from
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0x0100 to 0x10000. CO_FUTURE_ constants use bits starting at 0x20000. */
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#define CO_FUTURE_DIVISION 0x20000
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#define CO_FUTURE_ABSOLUTE_IMPORT 0x40000 /* do absolute imports by default */
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#define CO_FUTURE_WITH_STATEMENT 0x80000
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#define CO_FUTURE_PRINT_FUNCTION 0x100000
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#define CO_FUTURE_UNICODE_LITERALS 0x200000
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#define CO_FUTURE_BARRY_AS_BDFL 0x400000
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#define CO_FUTURE_GENERATOR_STOP 0x800000
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#define CO_FUTURE_ANNOTATIONS 0x1000000
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/* This value is found in the co_cell2arg array when the associated cell
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variable does not correspond to an argument. */

‎Include/compile.h‎

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@@ -18,12 +18,18 @@ PyAPI_FUNC(PyCodeObject *) PyNode_Compile(struct _node *, const char *);
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CO_FUTURE_UNICODE_LITERALS | CO_FUTURE_BARRY_AS_BDFL | \
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CO_FUTURE_GENERATOR_STOP | CO_FUTURE_ANNOTATIONS)
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#define PyCF_MASK_OBSOLETE (CO_NESTED)
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/* bpo-39562: CO_FUTURE_ and PyCF_ constants must be kept unique.
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PyCF_ constants can use bits from 0x0100 to 0x10000.
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CO_FUTURE_ constants use bits starting at 0x20000. */
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#define PyCF_SOURCE_IS_UTF8 0x0100
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#define PyCF_DONT_IMPLY_DEDENT 0x0200
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#define PyCF_ONLY_AST 0x0400
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#define PyCF_IGNORE_COOKIE 0x0800
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#define PyCF_TYPE_COMMENTS 0x1000
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#define PyCF_ALLOW_TOP_LEVEL_AWAIT 0x2000
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#define PyCF_COMPILE_MASK (PyCF_ONLY_AST | PyCF_ALLOW_TOP_LEVEL_AWAIT | \
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PyCF_TYPE_COMMENTS | PyCF_DONT_IMPLY_DEDENT)
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#ifndef Py_LIMITED_API
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typedef struct {

‎Lib/__future__.py‎

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@@ -68,14 +68,14 @@
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# this module.
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CO_NESTED = 0x0010 # nested_scopes
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CO_GENERATOR_ALLOWED = 0 # generators (obsolete, was 0x1000)
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CO_FUTURE_DIVISION = 0x2000 # division
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CO_FUTURE_ABSOLUTE_IMPORT = 0x4000 # perform absolute imports by default
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CO_FUTURE_WITH_STATEMENT = 0x8000 # with statement
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CO_FUTURE_PRINT_FUNCTION = 0x10000 # print function
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CO_FUTURE_UNICODE_LITERALS = 0x20000 # unicode string literals
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CO_FUTURE_BARRY_AS_BDFL = 0x40000
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CO_FUTURE_GENERATOR_STOP = 0x80000 # StopIteration becomes RuntimeError in generators
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CO_FUTURE_ANNOTATIONS = 0x100000 # annotations become strings at runtime
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CO_FUTURE_DIVISION = 0x20000 # division
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CO_FUTURE_ABSOLUTE_IMPORT = 0x40000 # perform absolute imports by default
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CO_FUTURE_WITH_STATEMENT = 0x80000 # with statement
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CO_FUTURE_PRINT_FUNCTION = 0x100000 # print function
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CO_FUTURE_UNICODE_LITERALS = 0x200000 # unicode string literals
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CO_FUTURE_BARRY_AS_BDFL = 0x400000
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CO_FUTURE_GENERATOR_STOP = 0x800000 # StopIteration becomes RuntimeError in generators
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CO_FUTURE_ANNOTATIONS = 0x1000000 # annotations become strings at runtime
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class _Feature:
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def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):

‎Lib/test/test_future.py‎

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@@ -1,5 +1,7 @@
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# Test various flavors of legal and illegal future statements
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import __future__
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import ast
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import unittest
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from test import support
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from textwrap import dedent
@@ -74,6 +76,21 @@ def test_badfuture10(self):
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from test import badsyntax_future10
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self.check_syntax_error(cm.exception, "badsyntax_future10", 3)
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def test_ensure_flags_dont_clash(self):
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# bpo-39562: test that future flags and compiler flags doesn't clash
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# obtain future flags (CO_FUTURE_***) from the __future__ module
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flags = {
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f"CO_FUTURE_{future.upper()}": getattr(__future__, future).compiler_flag
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for future in __future__.all_feature_names
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}
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# obtain some of the exported compiler flags (PyCF_***) from the ast module
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flags.update({
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flag: getattr(ast, flag)
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for flag in dir(ast) if flag.startswith("PyCF_")
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})
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self.assertCountEqual(set(flags.values()), flags.values())
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def test_parserhack(self):
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# test that the parser.c::future_hack function works as expected
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# Note: although this test must pass, it's not testing the original

‎Misc/NEWS.d/next/Core and Builtins/2020-05-01-14-58-16.bpo-39562.KCsX8n.rst‎

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The constant values of future flags in the :mod:`__future__` module are
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updated in order to prevent collision with compiler flags. Previously
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``PyCF_ALLOW_TOP_LEVEL_AWAIT`` was clashing with ``CO_FUTURE_DIVISION``.

‎Python/bltinmodule.c‎

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@@ -738,7 +738,7 @@ builtin_compile_impl(PyObject *module, PyObject *source, PyObject *filename,
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}
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if (flags &
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~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_DONT_IMPLY_DEDENT | PyCF_ONLY_AST | PyCF_TYPE_COMMENTS))
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~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_COMPILE_MASK))
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{
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PyErr_SetString(PyExc_ValueError,
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"compile(): unrecognised flags");

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